The present invention relates to apparatus for remote signaling to a telephone line over the available AC power line. More particularly, the present invention provides a telephone extension system for communicating over the AC power line between telephones of the system and a conventional telephone subscriber telephone line.
U.S. Pat. No. 3,949,172 which issued Apr. 6, 1976, entitled "Telephone Extension System Utilizing Power Line Carrier Signals", which is assigned to the same assignee as the present application, describes a system for doing very much the same thing as the system described in the present application. That patent describes a main (or master) station that couples the subscriber's telephone line to his AC power line and a special extension telephone that plugs into his AC power line at any convenient power receptacle and is used to make and receive telephone calls in a conventional manner. In that patent, the extension telephone includes a hand set with a microphone at one end and an earphone at the other with separate lines from each. The line from the microphone feeds a radio frequency (RF) transmitter and the line to the earphone comes from an RF receiver. A corresponding RF transmitter and RF receiver are provided at the main station. These transmitter-receiver combinations enable full duplex signalling of voice and other signals between the main station and the extension telephone over the AC power line.
The power line, RF carrier extension telephone system in U.S. Pat. No. 3,949,172 provides for a main (or master) station and one extension telephone that plugs into the AC power line at a power line receptacle. That system can accomodate more than one extension telephone and if all transmit at the same extension RF carrier frequency, the main can respond to any one of them. However, the single receiver at the main can respond to only one extension carrier at a time. It is an object of the present invention to provide such a power line carrier telephone extension system including several extension telephones that all can operate at the same time and engage in full duplex communication with each other and with the telephone line on telephone calls placed or received by any of the telephones of the system.
Signalling for other purposes than ordinary telephone usage between a conventional subscriber's telephone line and various kinds of transmit-receive devices over the available AC power line are described in U.S. Pat. No. 4,058,678, entitled "Remote Signaling to a Telephone Line Using Power Line Carrier Signals" (also assigned to the same assignee as the present application). That patent describes a system whereby appliances or other electrical equipment on the AC power line at a premises can be controlled by an incoming telephone call to the premises. The incoming telephone call brings control signals to the premises and these signals are carried by an RF carrier over the power line to the location of an appliance, for example, to turn the appliance on or off. The same patent describes a system for sending an alarm from the premises. For example, a fire detector in the premises plugged into the power line sends an RF alarm signal over the power line to the telephone where it initiates operation of the telephone to call a predetermined number and deliver a pre-recorded message. The systems in that patent can each accomodate more than one satellite station (appliance receiver controller or alarm transmitter) in operation at a time in conjunction with a single main station where the coupling between telephone line and power line is made, because the signalling is unidirectional (simplex). It is desireable where two or more of such systems are installed in a premises to integrate them with a single main station. Therefore, it is another object of the present invention to provide a technique of integrating such systems so that the satellite stations of both systems can be operated simultaneously.
Co-pending U.S. patent application Ser. No. 923,674, entitled "Utility Meter Reading via Telephone Lines and Power Lines Utilizing Power Line Carrier Signals" is a continuation-in-part of the application that issued as U.S. Pat. No. 4,058,678. It describes a system that signals in both directions by RF carrier over the power line in a premises, between the premises telephone line and a remote transmit-receive device on the power line that is controlled by the electric meter of the premises. The electric meter is addressed by the Electric Company from a remote telephone by calling the subscriber's phone and feeding electric meter interrogating signals to the subscriber's phone which are, in turn, transmitted over the subscriber's power line to his electric meter transmit-receive device, which responds by transmitting back the meter reading and any other information it is programmed to transmit. In this way, the electric meter is "read" by the Electric Company by a telephone call to the subscriber. Clearly, the remote transmit-receive device specially designed for this electric meter "reading", both receives and transmits information signals, but not necessarily simultaneously. This is called half duplex signalling. It is another object of the present invention to provide a technique of integrating or combining several such meter reading systems with each other and/or with an appliance control and/or an alarm system such as described above so that a single main station at the telephone line serves all the systems.
It is a further object of the present invention in conjunction with the above objects to provide an improved method and means of transmitting voice and data signals over a conventional AC power line at a typical telephone subscriber premises, whereby interference signals from other sources and noise on the power line are avoided.
It is another object to provide a multi-telephone extension system for a telephone subscriber's premises wherein system phones are capable of conferencing between the system phones and other functions such as the I, H, P, and S functions described herein, over a two element intra-premises transmission line.